Kinetic Energy Increase in Gases

Steps:

• Gas in fixed-volume container absorbs energy, raising its temperature.
• Internal energy of ideal gas depends only on temperature and kinetic motion of molecules.
• Added energy converts to increased average kinetic energy per molecule.
• Higher kinetic energy results in faster average molecular speeds.

Why B is correct:

• Kinetic molecular theory states that temperature is proportional to average kinetic energy (KE = 3/2 kT), so energy gain increases molecular speeds.

Why the others are wrong:

• A: Molecules are point-like and do not expand; only collective volume could, but container is fixed.
• C: Fixed volume prevents molecules from moving farther apart on average.
• D: Gas molecules primarily translate, not vibrate; vibration is negligible in gases at typical temperatures.

Final answer: B